关键词: 砂岩, 变形机制, 三轴压力, 脆延过渡

Abstract: The deformation mode and mechanism on two kinds of sandstone (feldspar sandstone and quartz sandstone) were experinmentally studied under confining pressure up to 700 MPa with strain rate of 10^-4/s.The transition field from brittle to ductile behavior in intact samples is respectively 200-400MPa PC and 250-350MPa PC for feldspar sandstone and quartz sandstone.A high pressure embrittlement phenomenon, however, appears above 600MPa P_C in feldspar sandstone. The transition boundary from stable sliding to stick slip in sawcut samples is 200MPa P_C and 150MPa P_C respectively for two kinds of sandstone.Microscopic observation results show that all of these deformation modes result mainly from the cataclasis mechanism in different grade. Cataclastic faulting results in brittle failure under low confining pressure. Homogenized cataclasis (cataclastic flow) inter and intra grains results in ductile flow. The relocalization of microcracking results in the embrittlement up to high confining pressure. The transition from brittle to ductile behavior is mainly due to the developing from faulting to homogenized cataclasis. As to the friction characteristics, the stable sliding is accompanying grains gliding on sawcut surface. The stick slip involves grains crushing severely. The transition from stable sliding to stick slip is between the both situation. Sometimes it is difficult to distinquish the different microstructural features for different friction modes.In this paper we also discussed the effects of mineral compositions on deformation mode and mechanism of rocks, the extension of brittle behavior in rocks, the two transitions from brittle to ductile and from ductile to embrittlement, the relation between cataclasis and deformation modes as well as the confusion of nomenclature in application to geology.

Key words: Sandstone, Deformation mechanism, Triaxial compression, Brittle-ductile transition